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Sept. 19, 2011 (Chicago) -- Researchers report that they have taken a small step toward developing a gene-based treatment that aims to control HIV without drugs in some patients -- and could lead to a "functional cure."

Researchers say a functional cure may occur when the patient would still be infected with HIV, but no longer needs drugs to control it and prevent disease.

The treatment involves genetically modifying CD4 cells -- immune system cells that are the target of HIV -- so that they are resistant to the virus.

In preliminary research, the new treatment was safe and well tolerated, says researcher Ronald T. Mitsuyasu, MD. Mitsuyasu is director of the University of California, Los Angeles Center for Clinical AIDS Research & Education.

HIV dropped to undetectable levels in one patient, even though he was taken off his usual antiviral medications, he tells WebMD.

"If we can get the immune system to kick in and control the virus without drugs, that's a win," Mitsuyasu says.

However, the treatment did not work as well in five other patients.

The findings were presented here at the 51st Interscience Conference on Antimicrobial Agents and Chemotherapy.

Targeting a Key Gene

The treatment, known as SB-728-T, disrupts the CCR5 gene used by HIV to enter and infect CD4 cells.

During the procedure, immune system cells are removed from the patient, modified, and reinfused.

The idea is to mimic naturally occurring CCR5 gene mutations that make cells resistant to HIV. The 5% of the population with two copies of the mutant CCR5 gene are basically immune to the virus. The 10% of people with one normal and one mutant CCR5 gene have a slower disease course.

Two studies presented at the meeting involved a total of 15 HIV-infected patients followed for about one year. There were no serious side effects related to the treatment, Mitsuyasu says. Still, long-term side effects are unknown.

In one study, six patients were taken off antiviral medication for 12 weeks after getting the new treatment. HIV levels dropped in three of them, and in one patient, HIV was no longer detectable.

That patient already carried a naturally occurring mutation in one copy of his CCR5 gene. That means that with the gene therapy, the patient had about twice as many gene-modified cells as other patients, Mitsuyasu says.

Indeed, the study showed that the greater the number of cells that carried modified CCR5 genes, the lower the amount of HIV in the blood.

Challenges Ahead

Sangamo Bioscience Inc., which funded the work, says it will move ahead with a strategy to maximize the number of cells that can be genetically modified. One such approach would be to target patients who already have some mutated CCR5 genes.

"It seems the number of modified cells is more important than previously reported," says Laurent Kaiser, MD, head of the virology laboratory at University Hospitals of Geneva in Switzerland. Kaiser is also a member of the committee that chose which studies to highlight at the meeting.

While there are many challenges to be overcome before gene therapy can move from lab to bedside, Kaiser tells WebMD that "he is convinced it's a way to move forward."

"When you only treat with antiviral drugs, you are just stopping replication of the virus," he says.

With gene therapy, the hope is to create a reservoir of cells that are resistant to HIV infection and continue to proliferate, Kaiser says.

If the approach pans out in larger, longer studies, the treatment would offer a "functional cure," Mitsuyasu says.

These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.